timer

//  boost timer.hpp header file  ---------------------------------------------//

//  Copyright Beman Dawes 1994-99.  Distributed under the Boost
//  Software License, Version 1.0. (See accompanying file
//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

//  See http://www.boost.org/libs/timer for documentation.

//  Revision History
//  01 Apr 01  Modified to use new <boost/limits.hpp> header. (JMaddock)
//  12 Jan 01  Change to inline implementation to allow use without library
//             builds. See docs for more rationale. (Beman Dawes) 
//  25 Sep 99  elapsed_max() and elapsed_min() added (John Maddock)
//  16 Jul 99  Second beta
//   6 Jul 99  Initial boost version

#ifndef BOOST_TIMER_HPP
#define BOOST_TIMER_HPP

#include <boost/config.hpp>
#include <ctime>

// ctime標準庫裏面包含了time.h，time.h裏面有下面用到的CLOCKS_PER_SEC  宏
// The number of clock ticks per second
// #define CLOCKS_PER_SEC  ((clock_t)1000)

#include <boost/limits.hpp>

# ifdef BOOST_NO_STDC_NAMESPACE     //一般都是定義了，所以沒有用到。
    namespace std { using ::clock_t; using ::clock; }
# endif


namespace boost {

//  timer  -------------------------------------------------------------------//

//  A timer object measures elapsed time.

//  timer對象是用來計量已經流逝的時間。

//  It is recommended that implementations measure wall clock rather than CPU
//  time since the intended use is performance measurement on systems where
//  total elapsed time is more important than just process or CPU time.

//  建議如果實現測量最好是使用clock而不是CPU時間。因爲我們需要測量的是在系統上的運行的時間
//  而不是進程或者CPU上使用的時間。

//  Warnings: The maximum measurable elapsed time may well be only 596.5+ hours
//  due to implementation limitations.  The accuracy of timings depends on the
//  accuracy of timing information provided by the underlying platform, and
//  this varies a great deal from platform to platform.

//  需要注意的是。因爲實現的限制，最大的測量時間可能只有596.5+個小時。關於時間上的精度
//  主要是由當前的平臺提供，所以在平臺與平臺之間也存在了比較大的差異。

class timer
{
 public:
         timer() { _start_time = std::clock(); } // postcondition: elapsed()==0
//         timer( const timer& src );      // post: elapsed()==src.elapsed()
//        ~timer(){}
//  timer& operator=( const timer& src );  // post: elapsed()==src.elapsed()
  void   restart() { _start_time = std::clock(); } // post: elapsed()==0
  double elapsed() const                  // return elapsed time in seconds
    { return  double(std::clock() - _start_time) / CLOCKS_PER_SEC; }

  double elapsed_max() const   // return estimated maximum value for elapsed()
  // Portability warning: elapsed_max() may return too high a value on systems
  // where std::clock_t overflows or resets at surprising values.
  {
    return (double((std::numeric_limits<std::clock_t>::max)())
       - double(_start_time)) / double(CLOCKS_PER_SEC); 
  }

  double elapsed_min() const            // return minimum value for elapsed()
   { return double(1)/double(CLOCKS_PER_SEC); }

 private:
  std::clock_t _start_time;
}; // timer

} // namespace boost

#endif  // BOOST_TIMER_HPP

 

頭文件:
timer.hpp       使用boost::timer
iostream        使用std::cout  和  getchar
windows       使用Sleep

從創建t以來，中途休眠了5毫秒，然後花費了6毫秒